Variable stiffness morphing limb for amphibious legged robots inspired by chelonian environmental adaptations

Robotic vehicles capable of transition from aquatic to terrestrial locomotion face considerable challenges associated with propulsive efficiency and performance in each environment. Here we present a morphing amphibious robotic limb that combines the locomotor adaptations of sea turtles for swimming and tortoises for walking. The limb can transform between the streamlined morphology of a sea turtle flipper and the load-bearing geometry of a tortoise leg using a variable stiffness material coupled to a pneumatic actuator system. Herein, we describe the fabrication and characterization of the morphing limb, and quantitatively show how morphing between hydrodynamic and axial-load bearing states can enhance the locomotive performance of a single design over land and in water.